Scientists ask to see evidence behind relaxing UK’s Christmas Covid rules

Ministers are facing calls to publish scientific advice on the relaxing of Covid-19 rules over Christmas amid warnings that a single infectious guest could infect a third of those at a household gathering.

Under rules revealed by the prime minister on Tuesday, up to three households can form a “bubble” for five days over Christmas. It prompted a raft of scientists to speak out, warning that mixing will inevitably lead to an increase in infections come the new year, leading to deaths. Some said the government should have put greater emphasis on the dangers and potential control measures.

Now experts have called for the government to release advice given by the Scientific Advisory Group for Emergencies (Sage).

Prof Gabriel Scally, visiting professor of public health at the University of Bristol and a member of Independent Sage, said information from the government’s advisers was important to decisions about how to celebrate Christmas, adding: “People have got choice and agency in a lot of this and in order to be able to exercise those choices wisely they deserve to be able to see the scientific advice.”

Dr Simon Clarke, associate professor of cellular microbiology at the University of Reading, said: “We need to see the science that all of [the government’s] decisions are made on and this is no different.”

Sage meeting documents are released each Friday but Clarke called for more detailed information to be made public. “We never get to see the raw data, the stuff that is informing their decisions,” he said, saying this hinders the ability of external experts to question or scrutinise whether regulations are overbearing or effective.

But Dr Julian Tang, clinical virologist at the University of Leicester, said: “I do not think Sage will have evidence to show that enhanced mixing is going to be beneficial in terms of stopping the virus from spreading, if anything it will increase the virus spread … The reason that the government and Sage are … giving this amnesty of five days is more of a psychosocial, emotional side of what Christmas means to people.”

A government office for science press officer said Sage advice would be released as part of one of the regular weekly tranche of documents.

The calls came as Dr Adam Kucharski, an associate professor at the London School of Hygiene & Tropical Medicine, and a member of the government’s Scientific Pandemic Influenza Group on Modelling (SPI-M), told the Guardian that studies from the UK and the US suggested that if there is a single infectious person within a household, each of their household contacts will have, on average, about a 35% chance of getting the coronavirus.

“If there are three other people then on average that is about one additional infection you are going to get, if there are six people then on average that is two additional infections,” he said. “And you can see that once you start scaling up the numbers you have in your bubbles, that one initial infection can generate potentially quite a lot of secondary transmission.”

Speaking in a personal capacity, Kurcharski said it was difficult to predict how many more infections might result from the festive period, noting that while schools and many workplaces will shut, there is likely to be greater mixing between households. Other important factors include how prevalent the virus is by Christmas, the number of households mixing and whether people stick to forming exclusive bubbles.

“There is no magic rule that will make you safe. It is very much a gradient of risk,” he said. But the situation in the aftermath of Christmas also matters. “If we have this period where there is more risk of household clusters in bubbles, the question is what do people do in the period after that, where does that infection go subsequently?” he said. “I think that is really going to influence where we are going to end up in January.”